INVESTIGATION OF STRUCTURAL AND MECHANICAL BEHAVIOR OF AA6351/Gr/TiC/B4C/WC HYBRID METAL MATRIX COMPOSITES

Abstract

Pure materials, despite their widespread use throughout history, have been constrained by deficiencies in strength, toughness, corrosion resistance, wear resistance and hardness. Hybrid metal matrix composites (HMMCs), a leap forward in overcoming the inherent limitations of pure materials These limitations have catalysed the evolution of composite materials, specifically MMCs, which combine the strengths of distinct materials to form an advanced, hybrid composite. Hybrid MMCs are superior to pure materials due to their improved mechanical and wear properties. These composites amalgamate different elements, generating a balance of properties that far exceed those of their individual constituents. Metal Matrix Composites (MMCs) offer a unique blend of properties by incorporating high performance reinforcements into a metallic matrix. To achieve this composite structure, various fabrication techniques exist, each with its own advantages and limitations. Powder metallurgy offers precise control over the reinforcement distribution but can be expensive and time-consuming. Friction stir processing utilizes friction heat to develop the composite, but its applicability is limited to specific shapes. In-situ processing mix the reinforcement while melting the matrix, but often requires complex process control. Squeeze casting offers good density control but can be restricted in terms of part geometry. This study specifically focuses on stir casting for the fabrication of MMCs due to its twin benefits of versatility and cost-effectiveness. Stir casting employs a mechanical stirrer to uniformly distribute reinforcement particles within the molten metal matrix. This relative simplicity translates to lower production costs compared to other techniques. Moreover, stir casting allows for the incorporation of a wider range of reinforcement types and volume fractions, making it highly adaptable for the creation of MMCs with diverse properties. By achieving a good balance between quality and affordability, stir casting becomes a favourable choice for a wide array of MMC production applications. To get the enhanced mechanical and wear characteristics, four reinforcements: Graphite (Gr), Boron Carbide (B4C), Titanium Carbide (TiC), and Tungsten Carbide (WC) were selected. Four sets of hybrid MMCs were fabricated: AA6351/Gr/B4C, AA6351/Gr/TiC, AA6351/Gr/WC, and AA6351/B4C/TiC/WC. The proportion of each reinforcement varied equally from 0.5 to 2.0 wt% in each set. Samples were prepared through stir casting process followed by basic machining processes. The composites that were produced went through a thorough characterization and testing process. The microstructure of the composites was examined using scanning electron microscopy (SEM) and optical microscopy to determine the distribution and bonding of the reinforcing phases within the metallic matrix. This analysis helped evaluate the effectiveness of the stir casting process. The mechanical properties of the composites were assessed through hardness testing, impact testing, tensile testing, and wear testing. These tests provided information on the composites' resistance to indentation, toughness, strength, deformation behavior, and wear resistance. A comparative analysis was also performed to understand how different reinforcing phases influenced the mechanical properties of the composites. By examining the hardness values, impact strength, tensile properties, and wear resistance of the different configurations, insights were gained into the performance of the composites. Finally developed composites were raked using TOPSIS method. Through comprehensive characterization, it was observed that the developed hybrid MMCs exhibited superior mechanical and wear properties compared to pure materials. In set 1, The lowest density, 2.62 g/cc, was found in the sample AlGrB05 having 2 wt% each of Gr and B4C. The hardness of hybrid metal matrix composite having 1 wt% Gr and 1 wt% B4C recorded the highest of 82. Sample AlGrB03 has the highest impact strength of 32 Joules. Sample AlGrB03 shows the highest engineering ultimate tensile strength and true ultimate tensile strength as 134.3 MPa and 167.0 MPa in comparison to other samples. In set 2, Due to the presence of graphite and porosity in the fabricated samples, the density of the aluminium metal matrix decreased. The samples with a reinforcement proportion of 2.0 wt% graphite and 2.0 wt% TiC exhibited the lowest density of 2.61 gram/cc. The maximum levels of hardness, impact strength, engineering ultimate tensile strength, and true ultimate tensile strength were observed at a weight percentage of 1.0 wt% for both Gr and TiC, with values of 85 HRC, 33 Joule, 206.7 N/mm2 , and 260.43 N/mm2 respectively. In set 3, incorporating graphite and tungsten carbide into the composite led to enhancements in both microstructure and mechanical properties. The lowest density was observed with 0.5 wt% Gr and 0.5 wt% WC as 2.73 g/cc. A uniform dispersion of reinforcement particles was observed. The sample reinforced with 1 wt% Gr and 1 wt% TiC demonstrated the highest tensile strength and hardness as 199.2 N/mm2 and 76 HRC, respectively. On the other hand, the composite that contained 0.5 wt% graphite and 0.5 wt% tungsten carbide of both reinforcements exhibited the best toughness as 28 joules, among all the samples that were produced. In set 4, lowest density was recorded with 0.5% of each reinforcement while in the hybrid metal matrix composite composed of 1.5 wt.% B4C, 1.5 wt.% TiC, and 1.5 wt.% WC, the highest tensile strength of 140.7 MPa, and hardness of 76 HRC are observed. Conversely, the hybrid metal matrix composite with 0.5 wt.% of each reinforcement exhibits the maximum toughness of 28 Joules. These research findings offer valuable insights for the design and development of high-performance metal matrix composites with potential applications in industries such as aerospace, automotive, and manufacturing. In TOPSIS test AlGrT03 ranked 1 due to its excellent mechanical characteristics. The tribological characteristics of hybrid Metal Matrix Composites reinforced with Gr and TiC surpass others, attributed to the effective bonding between the reinforcement and the AA6351 matrix. The wear rate ranged from 0.007621 mm3 /m for Al6351 to 0.00592 mm3 /m for AlGrT03, showing the lowest wear. Additionally, the coefficient of friction increased with higher loads, with AlGrT03 exhibiting the lowest friction at 40 N, measured at 0.374286. Microphotographs revealed the least debris and plowing among the samples tested. Based on the findings, potential applications for the developed composites include automotive brake rotors and pistons, high-speed cutting tools and dies, aerospace components such as engine parts and landing gear, and defence applications requiring armour and ballistic-resistant materials. These composites offer superior mechanical and wear characteristics, making them suitable for demanding environments that demand exceptional performance. The use of a low proportion of reinforcement, which has shown favourable results, further enhances the cost-effectiveness and viability of these composites in various industries.